As it is known, managing a communication network provides to perform a number of operations (which are termed “management operations” in the following description), such as for instance:                monitoring network performance;        configuring network elements and their resources (boards, ports, cross-connections, etc.);        managing errors occurring in the network; etc.        
Typically, the management operations are performed by an apparatus which is termed “network management station or system” (or, briefly, NMS), which is connected to each network element of the network to be managed.
In particular, the NMS is provided with a software application which is termed “manager”, capable of exchanging information with software applications which are termed “agent”, which agents are placed at the network elements. Manager and agents exchange each other management information by using a management protocol, which is dependent on the type of communication network. Examples of management protocols are SNMP (Simple Network Management Protocol), CMIP (Common Management Information Protocol), Q3, and TL1.
The NMS is typically capable of supporting one or more management graphic interfaces. Each management graphic interface allows an operator responsible of the network management to display management information relative to the network elements and their resources, such as for instance:                resource configuration parameters, i.e. the set of parameters which are defined by the operator upon activation of the resource (identifier, state, etc.);        resource performance parameters, i.e. the set of parameters which permit resource performance (rate, error rate, etc.) to be estimated during resource operation; and        alarms, i.e. management messages which are transmitted by the network elements to the NMS to indicate that an anomalous event has been detected (reduction of the power signal level, increase of the error rate, etc.).        
The NMS may receive from the communication network management information to be displayed through the management graphic interface according to a first mode which is termed “pull”, or according to a second mode which is termed “push”.
According to the pull mode, the operator generates by means of the NMS a request for receiving a certain set of management information from one or more network elements. For example, an operator can generate by means of the NMS a request for displaying configuration parameters relative to a certain resource of a network element (e.g., a port or a board). This causes the NMS to transmit to the network element a management message containing a request for receiving values of the configuration parameters relative to the resource. Upon reception of the request, the network element reads the currently stored values of the requested parameters from its local database and transmits them to the NMS by means of a reply message. In this manner, the NMS is capable of reading the reply message and using its contents to display the management graphic interface with the requested parameter values.
On the contrary, according to the push mode, when a given event occurs in the network, one or more network elements spontaneously transmit to the NMS a certain set of management information indicative of the event, thus notifying the operator of the event substantially in real time. The push mode is typically used for notifying the operator of events which occur in the communication network at times which are not predictable by the operator, such as for instance alarm generation or changing of one or more performance parameters. Generally, the NMS allows an operator to formulate one or more requests for monitoring a certain set of events, and to display corresponding notification messages on the currently open graphic interface. For example, an operator can formulate a request for monitoring time changes of the performance parameters of a certain resource. In this manner, the operator is notified substantially in real time of the possible time changes of the performance parameter value.